Diazo printing plates and method for the production thereof



United States Patent Ofiice 3,062,644 Patented Nov. 6, 19 62 Thisinvention relates to a novel presensitized printing plate containing adiazo compound, and to a method for the production thereof and, moreparticularly, to a novel presensitized printing plate which can bedeveloped merely by washing with water, thereby eliminating the alkalior acid treatment required with printing plates known to the prior art.

It is known that the solubility of water soluble colloids changes whenthe colloids are exposed to light in the presence of diazo compounds.However, the results of this hardening or tanning action are generallyunsatisfactory insofar as the practical use of such hardened colloids inthe reproduction art is concerned. It has, therefore, been proposed tosubject the colloid layers containing diazo compounds to anafter-treatment with a chromate solution after exposure to light under atransparent original or master. Diazo compounds of higher molecularweight, such as condensation products of aldehydes with diazo compounds,for example the diazo compound of p-amino-diphenylamine, have beenproposed for the tanning of colloid layers, and best results areobtained when these diazo compounds constitute about 10 percent byweight of the dry colloid applied.

However, the foregoing plates consisting of base materials coated withlayers consisting of water soluble colloids sensitized by means of diazocompounds, have not found practical application in the printing trade.The light-hardened colloid particles of these layers are not capable ofholding the greasy ink in flat and offset printing, and the mechanicalstrength of the hardened colloids is insufficient to permit long runs.

In accordance with the present invention, it has been found thatexcellent fiat and offset printing plates can be produced from lightsensitive material consisting of a support having a colloid layerthereon, the colloid layer comprising a polyacrylic acid and containingas light sensitive substances the diazonium chlorides or diazoniumbromides of 3-amino-carbazoles, i.e. 3-amino-carbazole and thesubstitution products thereof containing alkyl groups or alkoxy groups.Instead of polyacrylic acid,

there may be used polymethacrylic acid or copolymers ofacrylic-methacrylic acid.

Some of the diazonium salts to be used according to the presentinvention have been described in the literature. Insofar as theyconstitute new products, they can be prepared by the known methods ofdiazotization from the respective amino-carbazoles.

In practicing the present invention, sheet metal in the form of a plateor a foil, preferably sheet aluminum, or a paper sheet, preferably thespecific papers commercially available for the manufacture of paperprinting plates are used as base supports. For the purpose of providingthe base with the light sensitive layer, the respectivecarbazole-3-diazonium chloride or carbazole- 3-diazonium bromide, ormixtures of such diazoniurn salts, is dissolved in an organic solventand the solution is applied to the base by a whirling, spraying orbrushing operation. The coated layer supports are then dried, in

general at elevated temperatures, e.g. at about 90 C. 7

Suitable organic solvents are primarily solvents having a boiling pointbetween 80 and 150 C. Preferredare the ethylene glycol monoalkyl ethers,dioxane, and diacetone alcohol; the organic solvents may be mixed withwater and the mixture used for dissolving the 3-diazoniumcarbazole salt.The diazonium chlorides and the diazonium bromides obtained from the3-amino-carbazoles employed form, with polyacrylic acid andpolymethacrylic acid respectively, addition products which aredifficultly soluble in water. For this reason it is essential that thequantity of water added to the organic solvent be insufficient to causeseparation of the addition products. Advantageously, solutions of thediazonium salts are used which contain about 0.5 to 2 percent, byweight, of the respective diazonium chloride or bromide, or mixturesthereof. Although the weight ratio between the quantity of the colloidand the diazonium salt present in the solution may be varied within widelimits, it is preferred to use both components in approximately equalquantities, -i.e. 1:1.

The light sensitive colloidal layers produced according to thisinvention are of excellent stability and storageability. For makingprinting plates from the reproduction material, the colloidal layers areexposed to light under a light-image and after exposure an image isproduced on the support by merely developing it with water, e.g. byshowering or wiping the plate over with water or by immersing it in awater bath. Alternatively, the exposed plate may be developed byclamping it into the printing apparatus and wiping it over With a spongesoaked in Water. It is superfluous to subject the base after developmentto an after-treatment with dilute acid for the purpose of improving thewater conductivity of the surface of the base Where the colloidal layerhas been removed. Thus, a substantial simplification of the developingoperation is achieved. After the treatment with water (development), thecoated surface of the base is inked with greasy ink and the printingplates are ready for printing long runs of copies; faultless prints areobtained.

The following light sensitive compounds are exemplary of those which'maybe employed in the present invention:

Formula 1 OT O-m 01 N/ it Formula 2 NiBr Q CH3 Example I 0.6 part byweight of the compound corresponding to Formula 1 above and 0.6 part byweight of a watersoluble polymethacrylic acid (intrinsic viscosity==0.7)were dissolved in parts by volume of ethylene glycol monomethyl'ether.-This solution was coated on an alu- 100 C. for about two minutes.exposed to a negative light-image using an arc lamp of adding asaturated sodium chloride solution.

minum foil, the surface of which had been mechanically roughened. Thecoated foil was then dried and the drying operation was finished byexposing the coated surface of the foil to a current of hot air at atemperature of The sensitized foil was 18 amperes for two minutes, forexample, at a distance of 70 cm. The exposed surface of the foil wasthen rinsed with water and rinsing was continued until the yellowcoloredareas of the exposed coating, i.e. the areas unattected by light duringthe exposure, were removed completely, by the water; a positive image ofthe negative pattern remained on the foil and was clearly visible on theical Societ London, volume 121, page 2712. The diazonium chloride ispurified by dissolving it in water and The carbazole-3-diazoniumchloride is an orange-yellow powder, melting at 102-104 C. withdecomposition.

An equally good printing plate, giving runs of the same order, wasobtained by coating the aluminum foil with a solution containing, per100 cc. of ethylene glycol .monomethyl ether, 1.2 parts by weight ofcarbazole-3- diazonium chloride and 0.6 part by weight ofpolymethacrylic acid (intrinsic viscosity=0.7).

Example II An aluminum foil, the surface of which had been tmechanicallyroughened, was coated with a solution, conposed foil was eifected bymeans of tap water, see also Example I. From a negative pattern apositive printing plate was obtained.

The compound corresponding with Formula 3 may be substituted for thecompound of Formula 2 in the coating solution stated above. Thesensitized foil thus obtained is very stable and storageable over a longperiod of time.

The compound corresponding with Formula 2 above is made by diazotizing3-amino-6-methyl-carbazole in an aqueous hydrobromic acid solution;3-amino-6-methylcarbazole has been described by Bremer in JusticeLiebigs Annalen der Chemie, volume 514 (1934), page 279. The diazoniumbromide obtained is purified by dissolving it in water and by adding asaturated potassium bromide solution. The compound is an orange-yellowpowder which upon heating in a melting point tube, starts darkening at115 C. and decomposes at 170 C.

The compound corresponding with Formula 3 above is manufactured from3-amino-2-methoxy-carbazole. Because the statements relating to thepreparation of the starting material, contained in German Patent No.553,628, and also in Chemisches Zentralblatt, volume 32, II, page 1516,are somewhat ambiguous, 3-amino-2- methoxy-carbazole is prepared asfollows:

Z-methoxy-N-acetyl-carbazole (melting point 8184 C.) is obtained byheating a mixture of Z-methoxy-carbazole (melting point 233234 C.) andacetic acid anhydride at about 200 C. The acetylated product is treatedwith nitric acid at room temperature for several hours which treatmentresults in the formation of 2-mcthoxy-3nitro-N-acetyl-carbazole (meltingpoint 154-155 C.). This nitro compound is catalytically reduced withhydrogen and Raney nickel catalyst to 2-methoxy-3-amino-N-acetyl-carbazole (melting point ISO-181 C.). The amino-carbazoleobtained is heated with a 10 percent methanolic potassium hydroxidesolution for several hours, thereby splitting off the acetyl group. Theresulting 2-methoxy-3-amino-carbazole is separated in the form of itshydrochloride, which decomposes above 225 C. By diazotization of the2-methoxy-3-amino-carbazole hydrochloride in hydrobromic acid solution,Z-methoxycarbazole-3-diazonium bromide is obtained which is purified bydissolving it in water and by adding a saturated potassium bromidesolution. The diazonium bromide is a greenish-yellow powder which beginsdarkening and decomposing upon heating to about C.

Example III An anodically oxidized aluminum foil was coated with asolution containing, per 100 parts by volume of ethylene glycolmonomethyl ether, 0.6 part by weight of the compound corresponding toFormula 1 above and 0.8 part by weight of a water soluble polyacrylicacid of medium viscosity (intrinsic viscosity=0.5). Coating of thealuminum foil was effected by means of a conventional plate Whirler. Thefoil after being coated with the solution was dried, exposed to anegative light-image and, after exposure, rinsed with water for aboutone minute. A positive image was obtained which was inked up with greasyink. The foil could then be used as a printing plate.

Example IV The processed surface of a commercial paper printing foil wascoated With a solution containing, per 100 parts by volume of diacetonealcohol, 0.5 part by weight of the compound corresponding to Formula 2above and 0.7 part by weight of a water soluble polyacrylic acid ofmedium viscosity (intrinsic viscosity=0.5). The coated foil was driedand subsequently exposed to a light-image; after exposure, the exposedsurface of the foil was inked up with greasy ink and subsequently rinsedwith water. By this treatment with water, those areas of the acrylicacid layer which were not struck by light in the course of the exposure,were dissolved and the greasy ink sticking to the areas unaffected bylight was also removed. A positive printing plate is obtained if thelight-image used as a pattern is a negative.

Example V A zinc plate was treated with a 4 percent acetic acid solutioncontaining 4 percent by weight of potassium aluminum sulfate, thenbrushed for about 3 to 5 minutes, rinsed with water and dried. Then theplate was coated with a solution containing, per 100 parts by volume ofdiacetone alcohol, 2 parts by weight of the compound corresponding toFormula 2 above and 0.5 part by weight of a water soluble polyacrylicacid of medium viscosity (intrinsic viscosity=0.5). After coating, thesensitized plate was dried and exposed to a negative light-image. Theexposed plate was rinsed with Water and afterwards inked up with greasyink. Long runs of copies can be made from the positive printing platethus obtained.

Example V1 0.5 part by weight of the compound corresponding to Formula 1above and 0.5 part by weight of a water soluble copolymer of acrylicacid and methacrylic acid (molar ratio 1:1) were dissolved in 100 partsby volume of ethylene glycol monomethyl ether. An aluminum foil, bothsides of which had been mechanically roughened, was coated with thissolution. After the solution had dried, the coated side of the aluminumfoil was exposed under a negative transparent original and subsequentlyrinsed with tap water for about 30-60 seconds. Without furthertreatment, the imaged side of the foil was inked with greasy ink andused as a printing plate. A positive printing plate was obtained from anegative original.

The expression a polyacrylic acid as used in the following claims isintended to include a polymethacrylic acid as well as copolymerizates ofacrylic and methacrylic acid.

It will be obvious to those skilled in the art that many modificationscan be made within the scope of the present invention without departingfrom the spirit thereof, and the invention includes all suchmodifications.

What is claimed is:

1. A presensitized printing plate comprising a base material havingdirectly coated thereon a layer comprising a polyacrylic acid and acompound selected from the group consisting of the diazonium chlorideand bromide of a 3-amino-carbazole.

2. A presensitized printing plate comprising a base material havingdirectly coated thereon a layer comprising a polyacrylic acid and acompound having the formula in which X is selected from the groupconsisting of chloro and bromo ions and R is an alkoxy radical.

3. A presensitized printing plate comprising a base material havingdirectly coated thereon a layer comprising a polyacrylic acid and acompound having the formula N .aX

in which X is selected from the group consisting of chloro and bromoions and R is an alkyl radical.

4. A presensitized printing plate comprising a base material havingdirectly coated thereon a layer comprising a polyacrylic acid and acompound having the formula 5. A presensitized printing plate comprisinga base material having directly coated thereon a layer comprising apolyacrylic acid and a compound having the formula 6. A presensitizedprinting plate comprising a base material having directly coated thereona layer comprising a polyacrylic acid and a compound having the formula7. A process for developing a printing plate which comprises exposing tolight under a master a presensitized printing plate comprising a basematerial having directly coated thereon a layer comprising a polyacrylicacid and a compound selected from the group consisting of the diazoniumchloride and bromide of a 3-amino-carbazole, and washing the exposedplate with water.

8. A process for developing a printing plate which comprises exposing tolight under a master a presensitized printing plate comprising a basematerial having directly 6 coated thereon a layer comprising apolyacrylic acid and a compound having the formula NLX in which X isselected from the group consisting of chloro and bromo ions and R is analkoxy radical, and washing the exposed plate with water.

9. A process for developing a printing plate which comprises exposing tolight under a master a presensitized printing plate comprising a basematerial having directly coated thereon a layer comprising a polyacrylicacid and a compound having the formula in which X is selected from thegroup consisting of chloro and bromo ions and R is an alkyl radical, andwashing the exposed plate with water.

10. A process for developing a printing plate which comprises exposingto light under a master a presensitized printing plate comprising a basematerial having directly coated thereon a layer comprising a polyacrylicacid and a compound having the formula @gUNzCI and washing the exposedplate with water.

11. A process for developing a printing plate which comprises exposingto light under a master a presensitized printing plate comprising a basematerial having directly coated thereon a layer comprising a polyacrylicacid and a compound having the formula HaC N Br and washing the exposedplate with water.

12. A process for developing a printing plate which comprises exposingto light under a master a presensitized printing plate comprising a basematerial having directly coated thereon a layer comprising a polyacrylicacid and a compound having the formula NaBr N OCH: H

and washing the exposed plate with water.

13. A presensitized printing plate comprising a base material havingdirectly coated thereon a layer comprising a polyacrylic acid and acompound having the formula 3,062,844 7 coated thereon a layercomprising a polyacrylic acid and a compound having the formula R Y R1 52,593,928 N 2,772,974

References Qited in the file of this patent UNITED STATES PATENTS VonGlahn et a1 Nov. 28, 1950 Slifkin Apr. 22, 1952 Kosaiek et a1 Dec. 4,1956 Kosalek et a1 Feb. 4, 1958 Seven et a1 May 17, 1960 OTHERREFERENCES Saunders: The Aromatic Diazo Compounds, Edward Arnold & Co.,London, 1949, pages 7879.

1. A PRESENSITIZED PRINTING PLATE COMPRISING A BASE MATERIAL HAVINGDIRECTLY COATED THEREON A LAYER COMPRISING A POLYACRYLIC ACID AND ACOMPOUND SELECTED FROM THE GROUP CONSISTING OF THD DIAZONIUM CHLORIDEAND BROMIDE OF A 3-AMINO-CARBAZOLE..